One of my Fabia's remote key has stopped working, the battery has been changed, the red light comes on when the buttons are pressed and it will start the car, the other key works okay, what is the procedure for re syncing the key please.

Found this on an old post. You need two keys.

1. Switch Ignition ON and leave the key in the ignition.
2. Mechanically lock the vehicle from the Drivers door using the key to be coded.
3. Using the remote control press the Unlock button once, and the horn
will sound once.
4. Wait 6 seconds and press the unlock button once to activate the coding
procedure.

 

The remote control should now be programmed.

Have never tried it but worth a go

Alasdair